As used herein compositions are described by weight percent. To facilitate an understanding of this invention the variety of polymers discussed herein shall be referred to by their common acronyms as indicated below; however in the examples the acronyms refer to the specific polymers identified therein.
The term "PC" as used herein means an aromatic polycarbonate derived from the reaction of bisphenol-A and phosgene; such PC is commercially available from General Electric Company under the LEXAN trademark, from the Dow Chemical Company under the CALIBRE trademark and from Mobay Corporation under the MAKROLON trademark, including modifications of such polymers such as halogenated polycarbonate.
The term "PETG" as used herein means an amorphous polyester of terephthalic acid and a mixture of predominately ethylene glycol and a lesser amount of 1,4-cyclohexanedimethanol; such PETG was commercially available from Eastman Chemical Company under the KODAR trademark and is currently sold under the EKTAR trademark.
The term "PCTG" as used herein means an amorphous polyester of terephthalic acid and a mixture of predominately 1,4-cyclohexanedimethanol and a lesser amount of ethylene glycol, such PCTG was commercially available from Eastman Chemical Company under the KODAR trademark and is currently sold under the EKTAR trademark.
The term "PET" as used herein means a crystallizable polyalkylene terephthalate, i.e. a polyester of terephthalic acid and ethylene glycol; such PET is commercially available from The Goodyear Tire & Rubber Company under the CLEARTUF trademark.
The term "PBT" as used herein means a crystallizable polyalkylene terephthalate, i.e. a polyester of terephthalic acid and butanediol; such PBT is commercially available from General Electric Company under the VALOX trademark.
The term "ABS" as used herein means a graft rubber composition comprising a substrate of butadiene or copolymers of butadiene and styrene or acrylonitrile which substrate is grafted with styrene and acrylonitrile or derivatives thereof, e.g. .alpha.-methyl styrene and methacrylonitriles. ABS typically also comprises extractable styrene-acrylonitrile copolymer, i.e. copolymer not grafted to the rubber; such ABS is commercially available from Monsanto Company under the LUSTRAN trademark.
The term "ASA" as used herein means a graft rubber composition comprising a crosslinked acrylate rubber substrate e.g. butyl acrylate grafted with styrene and acrylonitrile or derivatives thereof, e.g. .alpha.-methyl styrene or methacrylonitrile, such ASA is commercially available from General Electric Company under the GELOY and/or LURAN trademark.
The term "MBS" as used herein means a graft rubber composition comprising a substrate of butadiene or mixtures of butadiene and styrene or acrylonitrile grafted with styrene and methacrylate; such MBS is commercially available from Rohm & Haas Company under the PARALOID trademark.
The term "AIM" as used herein means an acrylate impact modifier such as a graft rubber composition comprising a crosslinked acrylate rubber grafted with an acrylate thermoplastic; such AIM is as commercially available from Rohm & Haas Company under the PARALOlD trademark.
Nakamura et al. disclose in U.S. Pat. No. 3,864,428 blends of crystallizable polyester, such as polyalkylene terephthalates, e.g. PET or PBT, or polyalkylene naphthalates, PC and graft copolymers, e.g. MBS, having lower melt viscosity than PC alone.
Cohen et al. disclose in U.S. Pat. No. 4,257,937 blends of PBT (optionally PET), PC and polyacrylate.
Fromuth et al. disclose in U.S. Pat. Nos. 4,180,494 and 4,264,487 blends of PET, PC and AIM.
Lohmeijer et al. disclose in U.S. Pat. No. 4,654,400 blends of PC, PBT and AIM.
Blends of PET and/or PBT, PC and styrene-butadiene block copolymers are disclosed in U.S. Pat. Nos. 4,220,735, 4,239,677 and 4,111,895.
Chung et al. disclose in European Patent Application EP 0 108 996 A1 that impact properties of thermoplastic blends of polyalkylene terephthalate, e.g. PET, PC and an elastomeric based graft copolymer, e.g. ABS, are increased by the addition of a modifying oil. More specifically, Chung et al. illustrated that the addition of naphthenic oil (3.11%) improved the toughness of a blend of 64.2% PET, 14.2% PC and 21.4% ABS.
Allen et al. disclose in European Patent Application EP 0 111 810 A2 that a disadvantage associated with the use of polyalkylene terephthalate is its relatively low notched impact strength which carries over into blends of the polyester with PC. It is further disclosed that amorphous copolyesters e.g. PETG or PCTG, can be used in polycarbonate blends to improve in impact strength, transparency, processability, solvent resistance and environmental stress cracking resistance.
Boutni discloses in U.S. Pat. No. 4,628,074 blends of PC, PCTG and EPDM.
Ishihara discloses in U.S. Pat. No. 4,775,717 blends of PC and (graft modified) polystyrene having high heat resistance; improvements in melt viscosity are at the expense of toughness (e.g. see Table 1).
Lui discloses in U.S. Pat. No. 4,604,423 improving the impact strength of glass fiber-filled PC with a minor amount of amorphous polyester, e.g. PETG or PCTG and an olefin acrylate polymer.
Key properties for assessing the polymer blends of this invention are: melt flow into a mold as characterized by "Spiral Flow" (determined according to procedures set forth hereinbelow); heat resistance as characterized by heat distortion temperature under load (HDTUL) measured in accordance with ASTM D648; and impact resistance as characterized by notched Izod impact resistance of 8.2 cm (1/8 inch) thick samples (IZOD-1/8) and thick section notched Izod impact resistance of 6.4 cm (1/4 inch) thick samples (IZOD-1/4), measured at room temperature (23.degree. C.) in accordance With ASTM D-256.
Although polymer blends are prepared to provide a more desirable balance of properties as compared to the properties of the component polymers, there are often deficiencies in one or more properties of the polymer blend. For instance, a popular commercial blend comprises PC and ABS have higher heat resistance than ABS and reduced notch sensitivity in thick sections than PC; but a limitation of such blends have less than desired flow properties for many injection molding applications. Commercially available blends of PC and amorphous polyester have desirable heat resistance but low impact resistance, especially in thick sections, and less than desired flow properties for many injection molding applications. Blends of amorphous polyester and ABS have adequate flow properties but are generally so deficient in heat and impact resistance as to be undesirable as a molding resin.